Although his invitation was criticised as rewarding a "tyrant", Crown Prince Salman bin Hamad al-Khalifa was seen until recently as a reformist.

He had won key battles for influence over his father King Hamad over a conservative faction at court that vehemently opposed to political reform.

But last month the powerful prime minister, Sheikh Khalifa bin Salman, along with the two powerful brothers who run the military and the royal court's apparatus insisted on a crackdown backed by neighbouring Saudi Arabia.

"The Crown Prince should not be seen as someone who is representative of ongoing events in Bahrain today," said Theodore Karasik, of the Institute for Near East and Gulf Military Analysis.

"The Crown Prince was trying to broker a deal between the ruling family and the opposition and a lot of the reason the Saudis came in was to try to resolve disputes within the al-Khalifa family itself over this attempt by the Crown Prince."

The Crown Prince is in charge of the kingdom's economic portfolio but was seen as a rising power more generally.

He had faced down the prime minister, who is the king's uncle, on a number of pro-reform issues.

He was seen as backing a gradual move to democracy which has seen regular elections since 2002, though constituency boundaries prevent the majority Shia Muslim population gaining a majority in parliament. The ruling family is Sunni, as with all the Gulf monarchies.

The prince attempted to negotiate with protesters after an initial attempt to put down the unrest in February failed. But in mid-March, the army stormed protesters' encampments and tanks and troops from Saudi Arabia and the United Arab Emirates poured into the kingdom.

Since then, the prime minister, along with the military chief, Sheikh Khalifa bin Ahmed, another royal relative whose brother is the minister for the royal court, Sheikh Khalid bin Ahmed, have been leading the crackdown, in which 30 people have died and hundreds detained.

It has been reported Saudi Arabia's King Abdullah gave King Hamad no choice but to crack down and said he was sending in troops anyway.

The Saudi royal family fears that unrest from Bahrain's Shia population could spread into their own Shia minority in the oil-bearing east of the country, and any sign of weakness would spill over into anti-royal uprisings in other parts of the Arabian peninsula.

A high-level Saudi delegation, led by the king but also including the powerful hardline interior minister, Prince Nayef, is due to visit Bahrain later this week.

"We are seeing a lot more of the prime minister and the military chief in the local newspapers," one diplomat said. "This is indicative of who is in control at the moment."